Cellular network-based location system

ABSTRACT

In a cellular system configuration, the location of a mobile station is determined from the acquisition of cellular network data pertaining to the mobile station, and the translation of such network data into a corresponding geographical position profile. The cellular system includes a mobile station locator entity for receiving from a mobile switching center the network data such as cell and/or sector ID and trunk group member number. The mobile station locator translates the network data into position information such as geographic coordinates (latitude and longitude), resolution (radius), and angle values for sectorized cells.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of Reissue application Ser. No. 09/969,637 filedOct. 4, 2001, which is a continuation of Reissue application Ser. No.09/080,270 filed May 18, 1998, now U.S. Pat. No. Re. 38,267, which is areissue of U.S. Pat. No. 5,519,760, all of which are incorporated hereinby reference. Benefits under 35 U.S.C. 120 are hereby claimed.

FIELD OF THE INVENTION

The present invention relates to cellular communication systems and,more particularly, to a cellular configuration for determining thelocation of a mobile station.

BACKGROUND OF THE INVENTION

The increased terminal mobility offered by cellular telephone networksas well as mobile radio data networks has brought about an increaseddemand for location-based services and applications. Fleet operators areinterested in automated vehicle tracking applications to enhance theirdispatch operations. Moreover, stolen vehicle recovery systems haveenjoyed a significant amount of success during the past few years.However, most efforts to date have been designed around specializedequipment employed at the mobile operator site for acquiring locationinformation. For example, U.S. Pat. No. 5,043,736 to Darnell et al.discloses a cellular position locating system where the location of aremote unit is derived from data transmitted by a global positioningsystem to a specially equipped receiver at the remote unit.

SUMMARY OF THE INVENTION

The present invention concerns, in a cellular system comprising aplurality of cell sites each including a plurality of mobile stations incommunication with a base station, and comprising a plurality ofinterconnected mobile switching centers each in communication with thebase stations of certain cell sites, wherein each mobile switchingcenter maintains network identification data for each mobile stationbeing served in said certain cell sites, a method of determining thelocation of a mobile station originating communications within a cellsite, comprising the steps of: acquiring the network identification datafor said mobile station from the mobile switching center serving saidcell site; and translating said acquired network identification datainto geographical location information.

In another aspect the present invention concerns, in a cellular systemcomprising a plurality of cell sites each including a plurality ofmobile stations in communication with a base station, and comprising aplurality of interconnected mobile switching centers each incommunication with the base stations of certain cell sites, wherein eachmobile switching center maintains network identification data for eachmobile station being served in said certain cell sites, a method ofdetermining the location of a mobile station originating communicationswithin a cell site, comprising the steps of: transmitting from themobile switching center a cellular channel including the networkidentification data for said mobile station; receiving the transmittednetwork identification data; and translating the received networkidentification data into geographical location information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart depicting a communications sequence in accordancewith one embodiment of the present invention;

FIG. 2 is a flowchart depicting a communications sequence in accordancewith another embodiment of the present invention;

FIG. 3 is a block diagram of a mobile system configuration employing thepresent invention; and

FIG. 4 is a detailed block diagram representation of the mobile systemconfiguration in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The implementation of certain cellular services requires that the mobilestation location be made available to the service provider. For example,in a 911 emergency service, medical personnel need an accurate andprecise reading on the source of a distress call in order for promptmedical attention to be made available within the entire coverage areaof single or multi-carrier cellular networks. Although the locationfinding system disclosed by Darnell et al., supra, conveys highlyaccurate positional information from a modified mobile station speciallyconfigured to interface with a GPS system, a more desirable system froma subscriber perspective would keep intact the existing mobile stationconfiguration.

The present invention concerns an enhancement to the existing cellularnetwork topology permitting the acquisition of a mobile station locationusing cellular parameters from the network. The cellular parametersdefine the placement of each mobile station within its cellular networkand its relationship to other mobile stations. For example, theparameters may include data identifying the communications trunk groupserving the mobile station, a member number, and cell and/or sector ID.An accurate conversion of cellular data into a geographical profile maybe performed using radio plans as a translational mechanism. The radioplans, which correspond to geographic maps of radio coverage, furnishinformation such as the latitude and longitude derived from the cellbase station antenna location, elevation, radius, and angles forsectorized cells.

For purposes of discussion and clarity, the term “mobile stationlocator” (MSL or “Locator”) is used hereinafter to encompass a facility,mechanism, or assembly in whatever form implemented, constructed, oroperable, which interacts with and is the recipient oflocation-determinative cellular data from the cellular network. The MSLitself maintains an information resource responsive to input cellulardata for generating a corresponding geographical location estimate. Theresource is constructed by accumulating position data from radiocoverage maps, for example, where cellular data is translatable intogeographical information.

The basic configuration of a cellular network includes a plurality ofbase stations defining cell sites and providing wireless communicationto mobile station units within the cell site coverage area. The cellularnetwork is further configured with a plurality of mobile switchingcenters in communication with the base stations and other switchingcenters to perform processing and switching functions enablingconnections between mobile stations and interfacing to external networkssuch as the PSTN.

In one embodiment of the present invention detailed in the flow diagramsequence of FIG. 1, a code representing the identity of a mobile stationis transmitted from the mobile switching center (MSC or “Center”) to themobile station locator. In particular, the identity code corresponds toa mobile Identification Number (MIN) and/or an Electronic Serial Number(ESN). The Locator then queries the Center with the MIN, requestingnetwork data on the mobile station having the designated MIN. Inresponse to this query, the Center retrieves the requested informationsuch as trunk group and member number, and then forwards it to theLocator. A translation operation at the Locator converts the cellularnetwork data into corresponding geographical location information.

In another embodiment of the present invention detailed in the flowdiagram sequence of FIG. 2, cellular network data is transmitted alongwith the MIN from the Center to the Locator; accordingly, in thisembodiment, the Locator does not prompt the Center for cellular data. Ina preferred implementation, the Center invokes the transmission ofcellular data pertaining to a mobile station in response to a triggercommand from the mobile station represented by certain dialed mobiledigits known as a feature code.

FIG. 3 is a system level block diagram illustratively representing acellular configuration for implementing the present invention. Forpurposes of investigating the location-finding capability, an AssistanceCenter 31 was included to monitor the call from the mobile station andthe position information from the Mobile Station Locator (MSL) 32. Inparticular, AC 31 is an entity receiving a voice channel over a cellularlink connected to the Mobile Switching Center (MSC) 33, and receivingthe geographical location data from Locator 32. The Assistance Center 31includes a processing center with dispatching and/or storagecapabilities which receives user calls and location data and providesservices based upon that information. The Assistance Center 31specifically contains equipment which provides the capability for acall-taker (i.e., operator or dispatcher) to talk with the cellularphone caller and display the caller's position on a graphical display.

The Mobile Switching Center 33 is a cellular telephone network switchthat provides processing and switching functions to allow cellularphones to communicate with other phones (cellular and wireline). TheMobile Station Locator 32 is a facility performing the retrieval andstorage of location information pertaining to mobile stations. Inparticular, Locator 32 receives, retrieves, stores and processeslocation information, and then furnishes it to AC 31. The Locator 32 isequipped with an MSL-MSC Interface (MMI) that performs the retrieval oflocation information from the Mobile Switching Center 33.

Base stations, also called cell sites, are connected to Center 33 andprovide radio communication with the cellular phones. Base stations canbe configured with omnidirectional or sectorized antennas. An omni cellprovides radio coverage radiating out from the cell center in alldirections; this type of a cell may be approximated by a circle on amap. A sectorized cell has antennas which provide coverage for a sectionof the circle; this type of a cell may be approximated by a pie-wedgeshape on a map.

The cellular configuration shown in FIG. 3 was exercised during aLocation Assistance and Tracking Information Service (LATIS) field trialdemonstration to explore the methods by which the location of a mobilestation (e.g., cellular phone) originating a call may be made availableto entities both internal and external to the cellular network. TheLocator 32 principally serves the function of collecting location datafrom the cellular network, translating it, and providing it to AC 31.The location data comprised the geographic coordinates and size of theserving cellular network cell site (e.g., base station). The resolutionof this location data was limited by the size of the cell site; however,the resolution of the data from multiple cell sites was enhanced bysector information such as the cell subset/section.

The LATIS trial activated the acquisition mode to determine a mobilestation's position by engaging the operator into initiating a call into*the cellular network. In particular, the mobile station operator dialeda recognizable feature code (FC) on a standard cellular phone. TheCenter 33 recognized the feature code and connected the call to AC 31for establishing a voice connection between the answering personnel andthe caller.

The acquisition of location information by Locator 32, and itssubsequent delivery to AC 31, is accomplished during the LATIS trial bya first and second transport scheme hereinafter designated Methods I andII. In Method I, Center 33 transmits the caller's identity to AC 31 overa network connection. The caller's identity is defined by a MobileIdentification Number (MIN) which corresponds to the telephone number ofthe station originating a call. For the purposes of the trial, the MINwas ten (10) digits in length.

The AC 31 responds by forwarding to Locator 32 a message containing thecaller's MIN in order to request cellular data relevant to the MIN. TheLocator 32 then interacts with Center 33 to retrieve the cell-site trunkcurrently in use by that particular mobile station. The Locator 32converts the trunk information received from Center 33 into a locationvalue including a geographic coordinate (latitude and longitude), aresolution parameter (radius), and possibly two angle values (forsectorized cells). This information is then formatted and transmitted toAC 31 for graphical display. Depending upon the type of base stationcurrently serving the cellular phone, the location value may bedisplayed by AC 31 in different ways, such as with a circle described bythe geographic coordinate and the resolution, or a pie-wedge conveyingthis information and supplemented with the two angle values.

In Method II, Center 33 multiplexes the caller's identity (e.g., MIN)with cellular network data and transmits the combined signal to AC 31.For example, Center 33 may outpulse the MIN plus a 5-digit coderepresenting the serving cell/sector. The AC 31 receives this code andforwards it to Locator 32, which converts it into a geographicallocation value that is transmitted to AC 31 for graphical display. Thefollowing table summarizes the features of the transport methods usedduring the trial.

Location Mobile Dialed Digits Signaling Data Outpulsed Transport Method(Feature Code) from MSC to AC I *57 MIN (10) II 211 MIN (10) + cell &sector (5)

Although the LATIS field trial included specific routes forcommunicating cellular network data to Locator 32, these routes areindicated for illustrative purposes only and should not serve as alimitation of the present invention. Rather, the cellular network datamay be transmitted to Locator 32 directly or indirectly via any type ofcommunications link. Furthermore, the network data may be transmittedbefore or contemporaneously with the voice channel. For example, thevoice channel may be forwarded to AC 31 or another entity over one link,while the network data may be independently routed over an alternativepath to Locator 32. In addition, the MIN and/or network data (dependingupon the application) may be multiplexed with the voice channel beforetransmission from Center 33.

Likewise, even though in Method I the Locator 32 was prompted with theMIN by Assistance Center 31, and in Method II the cell/sector locationdata was initially transmitted to AC 31 before being coupled to Locator32 for conversion, this supervisory/coordinating role of AC 31 shouldnot serve as a limitation of the present invention. Rather, it should beapparent to those skilled in the art that the MIN for Method I and thecellular network data for Method II could be transmitted directly toLocator 32 from Center 33, while the voice communication would beseparately transmitted by Center 33 to AC 31 or any other end user.

FIG. 4 is a further block diagram representation of the cellularconfiguration in FIG. 3. The specific components, subsystems, and otherentities mentioned in conjunction with FIG. 4 should not be viewed as alimitation of the present invention, but as representative of oneimplementation of the cellular configuration. It should be apparent tothose skilled in the art that the functions demonstrated in FIG. 4 maybe implemented by other equivalent means.

The mobile station employed standard cellular phones such as Motorolatransportable cellular phones which did not require any non-standardmodifications. The phones were initialized with MINs (telephone numbers)from the serving GTE Mobilnet cellular system so that the phone would beon its “home” system throughout the trial.

The Mobile Switching Center 33 was an AT&T Autoplex System 1000comprising one Executive Cellular Processor (ECP) 41 and several DigitalCellular Switches (DCS) 42. Each DCS 42 is connected to several basestations (cell sites). The only hardware modification made to Center 33was the connection of a dedicated T-1 span (trunk group) to carry thetest calls to an Assistance Center Switch 43. The link between the DCS42 and ACS 43 is designated interface A in FIG. 4.

The ECP 41 was modified to provide the necessary digit translation, callrouting, and trunk signaling. The following discussion enumerates themodifications made to certain forms of ECP 41.

-   -   (1) The Subscriber and Feature Information Form was modified to        add Primary Dialing Class 22. The MIN of each test phone was        part of Dialing Class 22; this class was created for the trial        to restrict tile dialing capabilities of the test phones and to        prevent interference with the live traffic.    -   (2) Pattern matching was added to the Dialing Plan form (DPLAN).        These modifications specified the feature codes that were used.        If the dialed digits received form the mobile station matched        *57 (Method I), or 211 (Method II), a Destination Index of 911        for the DXDRTE route and a Dialed Number Modification (DNMOD) of        13 were assigned. If the digits matched *58+12 or more digits        (which would be latitude/longitude), a Destination Index of 911        and a DNMOD of 14 were assigned.    -   (3) Dialed Number Modification (DNMOD) 13 performed cell and        sector matching. If the call originated from one of the        cells/sectors in the table, a corresponding set of digits was        added to the dialed digits (*57 or 211), and the entire set was        routed to the Digit-By-Digit Call Routing (DXDRTE).    -   (4) Dialed Number Modification (DNMOD) 14 performed latitude and        longitude translation. The *58 was deleted from the incoming        digits, and the remaining lat/long digits were routed to the        Digit-By-Digit Call Routing (DXDTRE).    -   (5) The Digit-By-Digit Call Routing (DXDTRE) assigned an        outgoing trunk group and outpulsed the digits. The Feature Group        D signaling method was used. The caller's MIN was outpulsed in        the ANI (Automatic Number Identification) field, and the digits        sent by the DNMOD forms were outpulsed in the Called Address        field.

As noted above, Assistance Center 31 in FIG. 3 is equipped with meansfor communicating with the mobile station via the cellular network overa communications link such as a voice channel, and for receiving anddisplaying the geographical position information of the mobile stationcaller. The Assistance Center 31 is represented in FIG. 4 as anAssistance Center Switch (ACS) 43 and an Assistance Center DispatchStation 46, discussed infra. The ACS 43 contains telephone switchingequipment capable of receiving and discerning identity and locationinformation pertaining to incoming calls, and routing those calls tooperators as necessary.

The ACS 43 is configured to include a Summa Four SDS-500 switch 44 whichwas configured with two T1 cards, one used during the trial and theother used for testing. The ACS 43 may further include a dial tonegenerator, an MF (multi-frequency) card for inband signaling-datacapture, and an SLIC card to control attached telephone sets if sodesired. A dedicated T1 span (interface A) from Center 33 was connectedto one of the T1 cards; calls from Center 33 entered through ports onthis card. The SDS switch 44 was controlled by all SDS host 45 which wasrunning the SDS control software. The switch 44 communicatedswitch-related information and activity to the host 45 through reports;the host 45 issued commands to control the switch 44; and the switch 44responded to commands with responses. The SDS host machine 45 was anHP-9000 series workstation.

The control software for the switch 44 was written in the C programminglanguage and comprised five main modules (discussed infra) to executethe functions of receive messages, send messages, signal capture,analyze number, and prepare MSL input.

Receive Messages module

This module received messages from the SDS switch 44. This module wasdesigned to support different types of applications; based upon thedestination code and function ID in a message, the message was forwardedto an application module. For the trial, only one module, namely thesignal capture module, was used.

Send Messages module

This module received messages from host modules and queued them fortransmission to the switch. It returned several status responses to thecalling module, including socket full/output pending and communicationerror.

Signal Capture module

This module reacted to changes in the T1 and telset resources; thesechanges were sent to the host via Inpulse Rule Complete reports,Incoming Port Change reports, Outgoing Port change reports, or responsesto Outgoing Port Control commands. Based upon the report, a command wasbuilt and sent to the switch via the Send Messages module. The commandsincluded the resource's virtual communication address, and wereformulated with the SDS Application Program Interface (API).

The Inpulse Rule Complete report indicated that the signalinginformation from an inbound call (on the T1 span) was complete. Thereceived signaling data were then sent to the Analyze Number module foranalysis and further action.

Analyze Number module

This module analyzed the digits received by the signal capture module todetermine which set of location data it contained (e.g., latitude &longitude, cell & sector, or none). The location data were thenreformatted into a location information set and sent to the Prepare MSLInput module.

Prepare MSL Input module

This module prepared a location record for the MSL from the givenlocation information set. If any error in the location set was detected,an appropriate error message was written to a log file. Otherwise, adata record was passed immediately to Locator 32 via the Send Messagesmodule.

Additionally, this module sent an Outgoing Port Control command to theswitch to perform an Outpulse Rule (ringing, etc.) for an ACDS telset(discussed infra). Since six telsets were used, if the first one wasbusy, the second one rang; if they both were busy, the call was queued(with ringback heard by the caller), and the first available telsetreceived the call.

As noted above, the Assistance Center may also include an AssistanceCenter Dispatch Station (ACDS) 46 for housing telephone dispatchingequipment 47 that enables an operator to talk with a caller and processthe caller's location. This phone equipment would be interfaced to theSDS switch 44 through the SLIC card.

The ACDS comprised six standard telephones 47 and one HP-9000 seriesworkstation 48. The telephones 47, connected to the ACS 43, allowed theoperator to communicate with the callers/testers. Two softwareapplications ran on the workstation: a Geographic Information System(GIS) for electronic mapping of callers' locations and a Graphical UserInterface (GUI) which allowed the operator to quickly collect testscenario data.

The Geographic Information System is an X Window application whichdisplays geographic data. In addition, GIS contains highly powerfulalgorithms for determining the shortest route/path between any two ormore points. The following features were specifically added for use inthe trial.

-   -   A feature was added to display incoming location data with a car        icon; this corresponded with “exact” locations where latitude        and longitude data were present.    -   A feature was added to display incoming location data with a        circle; this corresponded with locations from omni-directional        base stations.    -   A feature was added to display incoming location data as a        pie-wedge (section of a circle); this corresponded with        locations from sectorized base stations.    -   Capabilities were added to retrieve and delete the information        related to a call. While any icon was illuminated, the operator        could click on the icon and retrieve the specific information        related to that call: MIN, latitude & longitude (if applicable),        and cell/sector values (if applicable). The operator could also        delete the entry, at which point the icon would be removed.

The GUI assists the operator in the gathering of necessary information.The GUI was built using X Windows/Motif 1.1 widget family, and includesa menu bar with twelve fields which the operator can fill with testinformation. The fields are delineated below.

-   -   (a) Dialing MIN: The tester's MIN.    -   (b) Date: The date and times were obtained from the        workstation's operating system.    -   (c) Dial Type: The dialing types (Method I or II) are listed.    -   (d) Cell: The name and number of the test cells were listed.    -   (e) Cell_id: The number of the cell used.    -   (f) Sector: The sector used by the tester in that cell.    -   (g) Caller: Caller's name.    -   (h) Call_taker: The operator's name.    -   (i) Weather: Four conditions were listed: sunny, partly cloudy,        rainy, and foggy.    -   (j) Location: Thirty-two pre-assigned test locations were        listed.    -   (k) Result: Pass or fail result was given to each test_index.    -   (l) Duration: Three call-duration times were listed: less than        ten seconds, less than one minute, and greater than one minute.

A comment field was also provided to function as a server for locationinformation. The Mobile Station Locator 32 was implemented with anHP-9000 series workstation.

The Locator 32 included an MSL Host & Server unit 49 containing softwarewritten in C and comprising the following six modules: main control,request, query-one, query-all, database-retrieval, GIS-interface. TheMSL server 49 was designed to handle multiple simultaneous calls andoperated as follows. The main control module waited for an incomingrequest from the ACS 43 (via interface B). For each incoming call, ifthe location data were present, the MSL server 49 translated it (ifnecessary) and formatted a data message which was sent to the ACDS 46.If the incoming call did not contain location data, the MSL server 49checked if information from a Mobile Switching Center was included; ifthe Center was known, Locator 32 interacted with that particular Centerusing the query-one module. If the Center was not known, Locator 32 hadthe capability to interact with all connected Mobile Switching Centersusing the query-all module. Both types of query modules were designed touse an MSL-MSC interface module 50, discussed below.

To ascertain the performance of the Mobile Station Locator 32, the maincontrol module recorded the following events, with time-stamps, in logfiles:

-   -   incoming mobile station call message received;    -   query sent to MSC interface process by the MSC query process;    -   query response received from the MSC interface process; and    -   mobile station location record sent to ACDS.

MSL-MSC Interface

The purpose of the MSL-MSC Interface (MMI) module 50 is to performMSC-specific processing to retrieve location information. The MMI 50 waswritten as an Expect script using TCL (Tool Command Language). The MMI50 login routine established a connection with the Autoplex ECP 41Recent Change port through the workstation's serial port. During thetrial, this connection involved dialing a modem and logging into the ECP41, all of which were handled automatically by the MMI 50. Once aconnection was established, the MMI 50 main program continuously scannedan input file for query requests from the MSL server 49.

When a query request was found, the MMI 50 would issue an OP:DN commandto the ECP 41; this command would contain the MIN received from Locator32 in the query request message. Under normal operating circumstances,ECP 41 would return an MCR (Mobile Call Register) value. The MMI 50would then issue an OP:MCR command with the MCR value. Under similaroperating circumstances, ECP 41 would return, among other data, the cellsite trunk information corresponding with the trunk currently servingthe mobile station. The MMI 50 returned this information (trunk groupand member number) to the MSL server 49 by writing it into an outputfile. If any errors were encountered, the MMI 50 would write anappropriate error message into the output file.

MSL Data Message Formats and Translations

The Locator 32 receives location data and performs conversions toprovide a uniform output message format to applications (API). Anillustrative output message format is as follows:

cell and sector 4 characters longitude 8 latitude 8 elevation 5 radius 5starting angle 5 real coverage angle 5 message/comments 125A space was used to delimit each field.

The MSL host 49 executes certain conversion operations to properlytranslate the cellular network identification data for a specifiedmobile station into geographical position information. For example,transport Method I provides trunk group and member number data from theMSL-MSC Interface 50 to the MSL host 49. This data is translated in afirst conversion operation into cell ID and sector ID information. In asecond conversion operation, employed as a principal operation fortransport Method II or as a secondary operation for transport Method I,the input data comprising cell/sector ID is converted into latitude andlongitude, resolution (radius), angle 1, and angle 2.

The conversion operations are preferably performed using indexabletables previously generated and stored at Locator 32. The data for thefirst conversion operation was obtained, for example, from lists oftrunk groups and member numbers used by each cell site (categorized bycell ID and/or sector ID). The data for the second conversion operationwas gathered from radio plans (geographic maps of radio coverage) forthe cells chosen for the trial, and organized into a tabular format. Thelatitude and longitude of each cell were taken directly from these radioplans using the base station antenna location as an index. The anglesfor sectorized cells were also extracted from the radio plans and othertables. The resolution of each cell/sector was determined from the radioplans as the distance from its center to the furthest point thatprovided at least −75 dB radio signal coverage. The −75 dB figure waspreferably used as a measure of the signal strength necessary to qualifyas a threshold for handoff.

The following describes the interfaces among the units represented inFIG. 4.

-   (1) MSC-ACS Interface (link “A”)    -   This is a T1 span with Feature Group D (FG-D) signaling. The MSC        33 outpulsed ANI (the mobile's MIN) and, depending upon the        location-transport method, a string of dialed digit which        contained information pertaining to the location of the caller.-   (2) ACS-MSL interface (link “B”)    -   This is a file-transfer interface between the SDS host 45 and        the MSL Server 49 processes. For all mobile-originated calls, a        request message including the mobile's MIN and optional location        information was written by the SDS Host 45 into a file. The MSL        server 49 read the data from the file. The SDS Host 45 and MSL        processes were executed on separate machines connected through        an ethernet link.-   (3) MSL-MSC interface (link “C”)    -   This is a serial connection between the MSL interface unit 50        and the MSC's recent change port. Since Locator 32 is located        remotely from Center 33, modems are used on a dial-up telephone        line. The MSL's MMI 50 interacted with the MSC 33 to retrieve        serving trunk group and member number data for a given MIN when        transport Method I is operational.-   (4) MSL-ACDS interface (link “D”)    -   This is a file-transfer interface between the MSL Server 49 and        the ACDS 46 application processes. The MSL writes its output        messages containing the geographic location information into a        file which is read by the ACDS application (GIS). Since the MSL        and ACDS processes are executed on separate machines, an        ethernet connection was used to transport the file read-write        messages.

As an alternative to the location-finding schemes discussed above, thegeographical location data may be obtained at the mobile station siteusing an enhanced mobile unit interfaced to an external positionlocation system such as a GPS satellite. Location data for this serviceconsisted of the latitude and longitude information uploaded by theenhanced mobile station. The resolution of this data was dependent uponthe capabilities of the positioning equipment used at the mobilestation.

For this service (designated transport Method III), an “enhanced”cellular phone employed an attached positioning device capable ofdetermining the current location of the mobile unit. At the mobileoperator's command, the enhanced phone read the current locationinformation from the positioning device and automatically initiated acall. The dialed digits comprised a feature code plus the latitude andlongitude location information. The Mobile Switching Center recognizedthis feature code and connected the call to the Assistance Center. Inparticular, the Switching Center outpulsed the MIN plus the latitude(‘lat’) and longitude (‘lon’) which were included in the digits dialedby the cellular phone; the ‘lat’ required eight digits, and the ‘lon’required seven digits. The Switching Center transmitted this informationto the Station Locator, which reformatted it and sent it to theAssistance Center for graphical display. Transport Method III issummarized in the following table.

Location Mobile Signaling Data Outpulsed Transport Method Dialed Digitsto AC from MSC III *58 + lon (8) + lat (7) MIN (10) + lon (8) + lat (7)

The implementation of transport Method III required certainmodifications to the mobile system configuration described above. Thefollowing discussion recites the enhancements made for the GPS-basedimplementation.

Enhanced Cellular Phones

Five GTE CCP-2000 Cellular Credit Card Phones (CCP) were modified foruse in the aforementioned LATIS trial to implement Transport Method III.The modifications included the software and hardware revisions notedbelow. Hardware modifications included the following.

-   -   The RJ-11 data jack on the side of the CCP was modified to        connect directly to the serial port of the CCP's microprocessor.        This allowed the CCP to communicate with an attached positioning        device via a serial link.

-   Several modifications were made to the CCP's operating software.    -   The software polled the serial port once every second looking        for location data from the connected positioning device. If data        was found and valid position information was included, the data        was flagged as valid and stored in a buffer. If no data was        found, or if invalid position information was included, the data        was flagged as invalid.    -   The software displayed a location status on the CCP's display.        If location data flag indicated valid data in the buffer, the        display would be updated with latitude and longitude information        alternating every five seconds. If the data was flagged as        invalid, an “Invalid Loc Data” message was displayed every five        seconds.    -   The function of the “Data” key was changed to provide the        following functionality. When the Data key was pressed by a        user/tester, the CCP would automatically initiate a call. The        dialed digits included a 3-digit programmable feature code (FC)        followed by 15 digits of position information (8 longitude        digits followed by 7 latitude digits). Once the call was        successfully initiated, control of the CCP was returned to the        tester.    -   The “Lock” key functionality was modified such that it would act        as a toggle for a Tracking Mode. If the Tracking Mode was        currently off when the Lock key was pressed, the CCP software        would enable the mode; if the mode was on when the key was        pressed, the software turned off the mode. While in the Tracking        Mode, the CCP software maintained complete control of the phone;        the tester could only press the Lock key, which would lead to        the mode being disabled and control returned to the tester.        While in the Tracking Mode, the CCP would initiate calls        automatically in a pre-programmed interval. The call initiation        was identical to that corresponding to the Data key press, but        the duration of the call and the time between calls were        determined by a set of programmable parameters.    -   The CCP's service utility was modified to allow the feature code        for the Data key to be programmed. Modifications were made also        to allow programming of the feature code, call duration, and        between-call interval for Tracking Mode.

The positioning devices were Lowrance OEM GPS receivers, although anysuch geographical positioning system may be employed. These receiverswere capable of receiving signals from location acquisition systems suchas GPS satellites, processing the signals, and computing a locationestimate based on those signals. One GPS receiver was connected to eachCCP-2000 phone through a serial data cable. The GPS receiversautomatically forwarded location information messages once every second.These messages contained the receiver status, position status, andposition information. The resolution of GPS receivers is highlydependent upon environmental factors and varies continuously. Undertypical conditions, a GPS receiver that is receiving data from three ormore satellites will have an accuracy of 50 to 100 meters.

While there has been shown and described herein what are presentlyconsidered the preferred embodiments of the invention, it will beapparent to those skilled in the art that various changes andmodifications can be made therein without departing from the scope ofthe invention as defined by the appended claims.

What is claimed is:
 1. In a cellular system comprising a plurality ofcell sites each including a plurality of mobile stations incommunication with a base station, and comprising a plurality ofinterconnected mobile switching centers each in communication with thebase stations of certain cell sites, wherein each mobile switchingcenter maintains network identification data for each mobile stationbeing served in said certain cell sites, a method of determining thelocation of a mobile station originating communications within a cellsite, comprising the steps of: acquiring the network identification datafor said mobile station from the mobile switching center serving saidcell site; and translating said acquired network identification datainto geographical location information using indexable tables generatedfrom data of trunk groups and member numbers used by each cell site anddata front geographic maps of radio coverage for said cell sites.
 2. Themethod as recited in claim 1 wherein the acquiring step includes thesteps of: transmitting from the mobile switching center a cellularchannel including an identity code assigned to the communicating mobilestation; prompting the mobile switching center with said identity codeto request network identification data for said communicating mobilestation; at the mobile switching center, responsively retrieving therequested network identification data using the identity code; andtransmitting the network identification data from said mobile switchingcenter.
 3. The method as recited in claim 2 includes the step of:developing an information array at the mobile switching center includingentries for each mobile station in said cell site indexed by arespective identity code.
 4. The method as recited in claim 2 wherein:said cellular channel further includes the mobile station communication.5. In a cellular system comprising a plurality of cell sites eachincluding a plurality of mobile stations in communication with a basestation, and comprising a plurality of interconnected mobile switchingcenters each in communication with the base stations of certain cellsites, wherein each mobile switching center maintains networkidentification data for each mobile station being served in said certaincell sites, a method of determining the location of a mobile stationoriginating communications within a cell site, comprising the steps of:transmitting from the mobile switching center a cellular channelincluding the network identification data for said mobile station;receiving the transmitted network identification data; and translatingthe received network identification data into geographical locationinformation using indexable tables generated from data of trunk groupsand member numbers used by each cell site and data from geographic mapsof radio coverage for said cell sites.
 6. A location-finding assembly ina cellular system, said system servicing a plurality of mobile stationsthrough a base station connected to a mobile switching center,comprising: server means responsive to a location request for promptingthe mobile switching center for network data on a base station; saidserver means including means for receiving network data from the mobileswitching center, and means for converting said network data into acorresponding geographical position profile using indexable tablesgenerated from data of trunk groups and member numbers used by each cellsite and data from geographic maps of radio coverage for said cellsites.
 7. In a cellular network, a method comprising: receiving anidentity and latitude and longitude coordinates of a mobile station,wherein the identity of the mobile station has been determined based onan emergency call from the mobile station and the latitude and longitudecoordinates of the mobile station have been provided by the mobilestation; using the latitude and longitude coordinates to determine whichtype of location data among multiple types of location data is usedduring the emergency call, wherein a first type of location data islatitude-and-longitude-coordinates-type location data; reformatting thelatitude and longitude coordinates to enable displaying the latitude andlongitude coordinates at an assistance center; and communicating theidentity and the reformatted latitude and longitude coordinates to theassistance center, which processes the emergency call using the identityand the reformatted latitude and longitude coordinates.
 8. The method ofclaim 7, wherein receiving the identity and the latitude and longitudecoordinates of the mobile station is from the assistance center.
 9. Themethod of claim 7, wherein receiving the latitude and longitudecoordinates is based on the mobile station placing the emergency call ata geographic position and the latitude and longitude coordinates reflectan approximate position of the mobile station.
 10. The method of claim7, wherein the mobile station that provides the received latitude andlongitude coordinates includes a Global Positioning System (GPS)receiver receiving information pertaining to the latitude and longitudecoordinates of the mobile station from one or more GPS satellites,wherein the mobile station is a cellular telephone.
 11. The method ofclaim 7, wherein receiving the identity and the latitude and longitudecoordinates of the mobile station is from a mobile switching center(MSC).
 12. The method of claim 11, wherein the latitude and longitudecoordinates provided to the MSC by the mobile station, which includes aGlobal Positioning System (GPS) receiver receiving informationpertaining to the latitude and longitude coordinates of the mobilestation, is from one or more GPS satellites, wherein the mobile stationis a cellular telephone.
 13. The method of claim 7, further comprisingreceiving updates to the latitude and longitude coordinates of themobile station after receiving the emergency call from the mobilestation.
 14. The method of claim 13, further comprising providingupdates to the assistance center by reformatting the updated latitudeand longitude coordinates and communicating the reformatted updatedlatitude and longitude coordinates to the assistance center.
 15. Themethod of claim 7, wherein the identity of the mobile station is atelephone number assigned to the mobile station.
 16. In a cellularnetwork, a method comprising: receiving an identity and latitude andlongitude coordinates of a mobile station, wherein the identity of themobile station has been determined based on an emergency call from themobile station and the latitude and longitude coordinates have beenprovided by the mobile station based on a geographic position of themobile station and the emergency call at the mobile station; using thelatitude and longitude coordinates to determine which type of locationdata among multiple types of location data is used during the emergencycall, wherein a first type of location data islatitude-and-longitude-coordinates-type location data; reformatting thelatitude and longitude coordinates to enable displaying the latitude andlongitude coordinates at an assistance center; and communicating theidentity and the reformatted latitude and longitude coordinates to theassistance center, which processes the emergency call using the identityand the reformatted latitude and longitude coordinates and maps theposition of the mobile station based on the reformatted latitude andlongitude coordinates for purposes of dispatching emergency personnel tothe position of the mobile station.
 17. In a cellular network, a methodcomprising: receiving a feature code and latitude and longitudecoordinates from a mobile station, wherein the feature code correspondsto an emergency call from the mobile station; determining an identity ofthe mobile station based on the feature code; using the latitude andlongitude coordinates to determine which type of location data amongmultiple types of location data is used during the emergency call,wherein a first type of location data islatitude-and-longitude-coordinates-type location data; communicating theidentity and the latitude and longitude coordinates of the mobilestation, wherein the communicated identity and latitude and longitudecoordinates assist an assistance center in locating the position of themobile station.
 18. The method of claim 17, wherein communicating theidentity and the latitude and longitude coordinates of the mobilestation to a mobile station locator that assists the assistance centerby providing data corresponding to the latitude and longitudecoordinates of the mobile station to the assistance center is forestablishing an approximate position of the mobile station.
 19. Themethod of claim 18, further comprising reformatting the receivedlatitude and longitude coordinates for communicating the reformattedlatitude and longitude coordinates to the mobile station locator. 20.The method of claim 17, wherein receiving the latitude and longitudecoordinates is based on the mobile station placing the emergency call ata geographic position and the latitude and longitude coordinates reflectan approximate position of the mobile station.
 21. The method of claim17, wherein the mobile station that provides the received latitude andlongitude coordinates includes a Global Positioning System (GPS)receiver receiving information pertaining to the latitude and longitudecoordinates of the mobile station from one or more GPS satellites,wherein the mobile station is a cellular telephone.
 22. The method ofclaim 17, wherein receiving the feature code and the latitude andlongitude coordinates of the mobile station from the mobile station viaa base station is associated with the mobile station.
 23. The method ofclaim 17, wherein receiving the feature code and the latitude andlongitude coordinates of the mobile station includes receiving asequential string of digits, the sequential string of digits including:a first string of alphanumerical characters representing the identity ofthe mobile station, and a second string of alphanumerical charactersrepresenting the latitude and longitude coordinates of the mobilestation.
 24. The method of claim 17, further comprising: recognizing thereceived feature code as corresponding to an emergency call; connectingthe emergency call to the assistance center in response to recognizingthe received feature code; and communicating the determined identity andreceived latitude and longitude coordinates of the mobile station to theassistance center.
 25. The method of claim 17, further comprisingreceiving updates to the latitude and longitude coordinates of themobile station after receiving the emergency call from the mobilestation.
 26. In a cellular network, a method comprising: receiving afirst string of alphanumerical characters representing a feature codeand a second string of alphanumerical characters representing latitudeand longitude coordinates from a mobile station, wherein the featurecode corresponds to an emergency call from the mobile station and thelatitude and longitude coordinates reflect an approximate position ofthe mobile station; determining an identity of the mobile station basedon the feature code; using the second string of alphanumericalcharacters to determine which type of location data among multiple typesof location data is used during the emergency call, wherein a first typeof location data is latitude-and-longitude-coordinates-type locationdata; communicating the identity and the latitude and longitudecoordinates of the mobile station, wherein the communicated identity andlatitude and longitude coordinates assist an assistance center inlocating the position of the mobile station.
 27. The method of claim 7,wherein the reformatting using the latitude and longitude coordinatesoccurs based on the determination.
 28. The method of claim 7, wherein asecond type of location data of the multiple types of location data iscell-and-sector-type location.
 29. The method of claim 16, wherein asecond type of location data of the multiple types of location data iscell-and-sector-type location data.
 30. The method of claim 17, whereina second type of location data of the multiple types of location data iscell-and-sector-type location data.
 31. The method of claim 26, whereina second type of location data of the multiple types of location data iscell-and-sector-type location data.